1. Field of the Invention
The present invention relates to sealing of semiconductor devices, and more particularly, to a method and apparatus for manufacturing a thermoplastic resin molded semiconductor device.
2. Description of the Related Art
As sealing material for semiconductor devices, transfer molding using thermosetting resin has been used. However, as thermoplastic resin having a high melting point and a high purity has recently been developed, transfer molding using this thermoplastic resin has been focused on as a sealing material for semiconductor devices.
In a prior art system for sealing a semiconductor device by transfer molding using thermoplastic resin, a semiconductor assembly formed by a semiconductor device (chip) and a lead frame is sandwiched by two metal molds so that the semiconductor assembly is located within a cavity between the metal molds. Then, hot thermoplastic resin is injected into the cavity and the injected thermoplastic resin is cooled and hardened by the metal molds, to thereby form an enveloper of thermoplastic resin for the semiconductor assembly, which will be explained in detail later.
In the above-mentioned prior art system, however, injection of thermoplastic resin is carried out through a runner and a gate passage (gate passages, if there are a plurality of semiconductor assemblies) which are also cooled by the metal molds so that thermoplastic resin therein is also hardened. Therefore, after the resin for the enveloper as well as for the runner and the gate passage is hardened, it is necessary to manually or antomatically remove the resin for the runner and the gate from that for the enveloper. If this is done automatically, a removing mechanism has to be provided in the system, which may cause the system to be large in size and complex. Also, since the resin is consumed in forming the runner and the gate passage, in addition to forming the enveloper, the efficiency of resin use is very low, for example, less than 60%, which may increase the manufacturing cost.